Paul Winkler wrote:
Martijn Faassen wrote:
Missing powerful query concepts
-------------------------------
Certain powerful query concepts like joins, available in a relational
setting, are missing. I've already run into a scenario where I wanted to
someting like this: given a bunch of version objects with field 'id',
where multiple objects can have the same 'id' to indicate they're
versions of the same object, I want all objects where field
'workflow_state' is 'PUBLISHED' unless there is another object with the
same id that have workflow_state 'NEW', in which case I want that one'.
I think joins would be a way to solve it, though I haven't figured out
the details, nor how to implement them efficiently on top of the
catalog. This kind of thing is where a relational database makes life a
lot simpler.
I used to have the same complaints in Zope 2, but so far I've been happy
with Dieter's AdvancedQuery product. See
http://www.dieter.handshake.de/pyprojects/zope/AdvancedQuery.html
It might be worth a look while thinking about what to implement for zope 3.
Here's Dieter's example from that page:
from Products.AdvancedQuery import Eq, Between, Le
# search for objects below 'a/b/c' with ids between 'a' and 'z~'
query = Eq('path','a/b/c') & Between('id', 'a', 'z~')
Something very similar to this I can also do with the layer I built on
top of Zope 3's catalog. It wasn't hard to write at all, which speaks
for the clean design of the Zope 3 catalog.
# evaluate and sort descending by 'modified' and ascending by 'Creator'
context.Catalog.evalAdvancedQuery(query, (('modified','desc'), 'Creator',))
This is interesting and my layer cannot do this yet.
# search 'News' not yet archived and 'File's not yet expired.
now = context.ZopeTime()
query = Eq('portal_type', 'News') & ~ Le('ArchivalDate', now)
| Eq('portal_type', 'File') & ~ Le('expires', now)
context.Catalog.evalAdvancedQuery(query)
In your example you haven't done a join as I describe above, unless I
miss something. The essential part is that I want an object with state
'PUBLISHED' unless there is another object where field 'ID' is the same
as this object that is with state 'NEW'. The join is in the 'ID'
matching part.
Regards,
Martijn
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